"Probably well over half of antibiotic prescriptions for acute respiratory infections are given for what are really viral infections, [and they do not affect the course of those infections]," says Storch, an expert in paediatric infectious disease.

"The physician cannot be sure in many cases that it's not a bacterial infection that requires antibiotics, so to be on safe side they prescribe antibiotics and this is very much responsible for the overuse of antibiotics."

Storch and colleagues took blood samples from 35 children who were suffering fever, and had tested positive for adenovirus, human herpesvirus 6, or enterovirus infection, or for acute bacterial infection.

They looked at the pattern of expression of all the genes in white blood cells, and compared the findings with data from 22 control children who had no fever.

"We found that we could make a classification and separate the bacterial and viral infections," says Storch.

Using a microarray with 47,300 probes, the researchers were able to identify 15,000 genes that gave a distinct pattern of expression depending on the type of infection. By further analysis, they were able to narrow this down to just 18 classifier genes.

The researchers validated their findings by applying them to data from a separate published study that looked at children suffering from other infectious diseases.

A test for the doctor

Storch says the team hopes to further decrease the number of classifier genes to speed up the development of practical technology for use by doctors.

"The possibility of designing a test so straight-forward that it could be done in a doctor's office is very real. I would be optimistic that it could happen within five years," says Storch.

"Right now the technology would be expensive, but I think there is every indication the costs could come down."

In the future, instead of measuring gene expression, the researchers may instead focus on detecting the proteins produced by the genes in a blood or urine sample.

Immunologist, Professor Shaun McColl from the University of Adelaide says the research is "heading in the right direction" and within five to 10 years a small chip that was able to analyse blood within an hour could be developed.

"That's a way down the track but I know there are companies working towards that," says McColl.